Method of increasing recovery of petroleum from subterranean formations

ABSTRACT

Tertiary or secondary waterflood method wherein there is injected into the formation prior to the main aqueous drive fluid a slug of a thickened aqueous solution and a slug of concentrated surfactant solution, said slugs being injected either as a mixture or sequentially.

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Campbell et al. 1 Nov. 6, 1973 [54] METHOD OF INCREASING RECOVERY OF 3,437,141 4/1969 Brandner ,1 [66/273 PETROLEUM OM SUBTERRANEAN- 3,446,282 5/1969 Cooke 166/274 3,520,365 7/1970 Jones 166/273 FORMATIONS 3,421,582 1/1969 Fallgattcr 1 166/273 [75] Inventors: David W. Campbell; Robert R. 3,5 3/197 ms 1 l66/2 3 Matthews, both f Ponca City, Okla 3,527,301 9 1970 Raifsnider.... 166 274 3,618,664 11/1971 Harvey 166/274 Asslgneer Continental Oil p y, Ponca 3,648,774 3/1972 Kirk 166/305 R City, Okla. [22] Filed; July 2, 1971 Primary Examiner Robert L. Wolfe Att .-.1 hC.l(t k' t'l. 21 Appl. No.2 159,522 Omey osep o d [57] ABSTRACT [52] US. Cl. 166/273 51 1111.01 E2lb 43/16 Tertiary or Secondary waterflood method wherein [58] Field of Search 166/273, 274, 275 there is injected into the formation prior to the main aqueous drive fluid a slug of a thickened aqueous solu- 5 References Cited tion and a slug of concentrated surfactant solution, said UNITED STATES PATENTS slugs being injected either as a mixture or sequentially.

3,638,728 2/1972 Hill 166/273 4 Claims, N0 Drawings METHOD OF INCREASING RECOVERY OF PETROLEUM FROM SUBTERRANEAN FORMATIONS BACKGROUND OF THE INVENTION the aqeuous medium through the formation toward one or more production wells similarly penetrating the formation. Formation fluids are recovered through the production wells. It has been suggested to inject a slug of thickened water ahead of the main body of waterflood medium. It has also been suggested to inject a slug of surfactant also referred to as a surface active or wetting agent ahead of the main body of waterflood medium or add such a surfactant to the main body of the waterflood medium. However, regardless of the particular waterflood technique used, a substantial part of the oil remains in place in the formation, i.e., is not recovered by the second recovery process.

It is an object of this invention to provide a secondary waterflood or tertiary recovery process wherein a higher proportion of the oil in the formation is recovered. It is a further object to provide such a process which recovers a given amount of oil in a shorter period of time. It is a still further object to provide such a process which recovers a given amount of oil by injecting a smaller volume of tertiary recovery medium. Other objects, advantages and features of the invention will become apparent from the following description and claims.

BRIEF SUMMARY OF TI-IEINVENTION The invention comprises a secondary or tertiary recovery process for a petroleum-bearing subterranean formation penetrated by a'plurality of wells comprising:

a. injecting into such a formation via an injection well a slug of a thickened aqueous solution,

b. injecting into the formation via the injection well a slug of concentrated surfactant solution,

c. injecting a waterflood drive solution, and

d. producing fluids from the formation via a production well.

The slug of a thickened aqueous solution may be injected prior to the slug of concentrated surfactant solution, or the two solutions may be mixed and injected as a single slug.

DESCRIPTION OF THE PREFERRED EMBODIMENTS One of the problems associated with previous waterflood methods has been that the flooding medium has often had a lower viscosity than the formation hydrocarbons being displaced. Thus the flooding medium tends to bypass or finger around a portion of the hydrocarbons which remain trapped in the formation. One way to alleviate this bypassing is by thickening or increasing the viscosity of the initially injected portion of the waterflood medium by adding therego any of a number of known thickeners such as polysaccharides, natural or artificial gums for example, guar gum, cellulose derivatives such as carboxymethyl cellulose, and water soluble partially hydrolyzed polyacrylamide polymers. Such polymers are preferred in that they not only thicken an aqueous waterflood medium but also have been reported to reduce a formations permeability to water while having little effect on oil permeability. This phenomenon may be desirable in some instances but is undesirable in others, such as injecting an aqueous drive fluid into a formation wherein the polymer may cause an undesirable decrease in the rate at which the drive fluid may be injected.

The partially hydrolyzed acrylamide polymers useful in this invention are well known in the art. They are water-soluble acrylamide polymers which have been hydrolyzed to such an extent that between about 0.8 and about 10 percent of the amide groups have been converted to carboxyl groups. In addition to homopolymers of acrylamide, watersoluble copolymers of acrylamide with up to about 15 percent by weight of other polymerizable vinyl compounds such as styrene, vinyl acetate, acrylonitrile, vinyl alkyl ethers, vinyl chloride, vinylidene chloride, methacrylamide, alkyl esters of acrylic and methacrylic acids and the like. These copolymers can conveniently be prepared using a polymerization catalyst such as benzoyl peroxide. The polymers should be of sufficiently high molecular weight so that a 0.5 percent by weight aqueous solution thereof has a viscosity of at least 4 and preferably at least 10 centipoises at 21.5 C as measured using an Ostwald viscometer. Such polymers and their use in waterflooding are described in the literature.

The thickened aqueous solution may be made from fresh water but is often a brine solution such as a solution of sodium chloride or other salt in water. The brine may be prepared by adding the desired salts to water or there may be used a natural brine such as one produced from a subterranean formation or present in a lake or other body of water. Enough thickener is added to increase the viscosity of the aqueous solution to at least about 1 centipoise. Preferably the aqueous solution should have a viscosity approximately equal to the viscosity of the oil in the formation, e.g., about 10 to 1,000 cps. The amount of thickener required to achieve such a viscosity depends on the particular thickener employed and is well known in the art. Generally from 0.1 to 1.5 percent by weight thickener is satisfactory. With the especially effective polyacrylamide type thickeners from 0.03 to 1.0 percent by weight can be used. Below the suggested lower limits the viscosity of the composition is not increased enough to be more effective than nonthickened compositions. Above the suggested upper limits the viscosity of the composition becomes so great that it is difficult to inject the composition through the formation. The size of the slug should be 2 to 20 percent of the pore volume. Slug sizes of less than 2 percent of the pore volume are too small to maintain their integrity when passed through the formation a significant distance, i.e., due to their small size they tend to breakdown quickly and allow the subsequently injected drive fluid to finger through. Slug sizes of more than 20 percent of the pore volume become quite expensive. It is more economical and just as effective to push the slug through the formation with an unthickened drive fluid rather than to further increase the slug size.

It is also known in various waterflooding procedures to inject a surfactant or surface active agent along with the aqueous drive fluid. Any of a wide variety of watersoluble surface active agents may be used. These include anionic, nonionic, cationic and amphoteric types. For example:

A. NONIONIC l. Products obtained by autocondensation of various fatty matter and their derivatives with ethylene oxide, propylene oxide, glycols, or glycerols:

a. a fatty acid plus ethylene oxide or glycerol, such as palmitic acid plus 5 moles ethylene oxide or glycerol monostearate;

b. an alcohol plus ethylene oxide, such as hydroabietyl alcohol plus 15 moles ethylene oxide;

c. an ester or aldehyde plus ethylene oxide;

d. an amide or amine plus ethylene oxide, such as diethanolamine plus 15 moles ethylene oxide.

ll. Products obtained by condensation of phenolic compounds having lateral chains with ethylene or propylene oxide. Examples are disecbutyl phenol plus moles ethylene oxide and octyl phenol plus 12 moles ethylene oxide.

B. CATIONIC l. Neutralization product of primary, secondary or tertiary amine with an acid such as trimethyl octyl ammonium chlorides, lauryl dimethyl benzyl ammonium chloride and the like, commonly referred to as quaternary ammonium chlorides.

C. ANlONlC l. Alkyl aryl sulfonates such as ammonium isopropyl benzene sulfonate;

ll. Fatty alcohol sulfates such as sodium 2 methyl 7- ethyl 4 hendecyl sulfate;

lll. Sulfated and sulfonated amides and amines such as sodium N methyl N oleyl taurate;

IV. Sulfated and sulfonated esters and ethers such as dioctyl sodium sulfo succinate;

V. Alkyl sulfonates such as sodium dodecyl sulfonate.

D. AMPHOLYTIC l. Molecules where the molecule as a whole forms a zwitterion, such as cetylaminoacetic acid.

A reference book which describes many types of surfactants suitable as foaming agents is Surface Active Agents and Detergents," Volumes I and II, by Schwartz et al., lnterscience Publishers.

Especially useful is a di-n-alkaryl sulfonate, more specifically a di-n-alkylbenzene sulfonate, wherein the alkyl groups have from 1 l to 15 carbon atoms. The sulfonate is neutralized with sodium hydroxide. This material is referred to as Sulfonate A in the tests described below.

The concentrated surfactant solution may also be made using either fresh water or a brine. The concentration of the surfactant in the aqueous medium should be from about 5 to about 50 percent by weight, preferably from 10 to percent. Solutions containing less than the minimum suggested amount of surfactant are relatively ineffective in removing oil from the formation. Solutions containing more than the maximum suggested amount of surfactant do not result in the recovcry of a correspondingly greater amount of oil and are therefore unnecessary. The size of the slug should be 0.5 to 10 percent of the pore volume. The reasons for the suggested range of pore size are the same as discussed above in connection with the thickened aqueous liquid.

Primary oil recovery results when the oil flows from the well naturally or can be removed by pumping. Secondary oil recovery results from the injection of some agent into the formation during or preceding production, such as a waterflood, gaseous or miscible drive fluid, in situ combustion and the like. After the secondary recovery operation, some oil still remains in the formation. Attempts to remove this remaining oil by further treatment is referred to as tertiary oil recovery.

It has been reported by some sources that injection of a thickened aqueous solution into the formation in a secondary recovery operation results in the recovery of some oil. However, this same composition used in a tertiary oil recovery process produces little or no tertiary oil. Injection of a surfactant slug followed by a drive fluid following a secondary recovery operation results in the production of some tertiary oil. The basis for this invention is that a surprisingly large amount of tertiary oil can be recovered following a secondary recovery operation if there is then injected into the formation a slug of a thickened aqueous solution followed by a slug of a concentrated surfactant solution, such slugs being injected either sequentially or after having been mixed together, and-finally followed by an aqueous drive fluid. The reason for this improved recovery of tertiary oil is not completely understood. it is postulated that perhaps comicellization of the thickener of the thickened aqueous solution with the surfactant may occur. Thus the two components may stabilize each other against adsorption onto the formation rock allowing the tertiary recovery fluid to flow through the formation with a minimum amount of undesirable adsorption which can deplete the tertiary recovery fluid of its active components thus decreasing its effectiveness. Another possibility is that the surfactant may adsorb on the thickener of the thickened aqueous solution allowing the latter to act as a carrier to transport the surfactant through the formation with a minimum of undesirable adsorption onto the formation. Regardless of the mechanism involved, the use of the two treating agents together followed by a drive fluid results in a surprisingly greater tertiary oil recovery than if either one alone precedes the drive fluid.

EXAMPLES To evaluate the procedures of this invention, the following laboratory ,tests were made. The lateral surface of a linear Berea sandstone core 12 X 2 X 2 inches, having a permeability of from 150 to 200 millidarcies and a pore volume of 145 cc, was coated with epoxy resin. The core was then positioned in a pressurized bomb so that fluid could be forced in one end of the core and out the other end. The core was first evacuated. Next, a brine containing 5 percent by weight sodium chloride was injected into the core under pressure to saturate the core. Next, pale oil was injected until no more brine was produced from the core. Pale oil is a solventrefined Mid-Continent oil. Eighty pale oil has a viscosity of 80 sabolt seconds universal at F. Since no more water could be produced from the core, it was said to be at irreducible water saturation, lWS. The 5 percent sodium chloride brine was again injected into the core until no more pale oil was produced. The oil that was produced during this step is called secondary oil. At this point a slug of various additive was injected What is claimed is:

l. A tertiary oil recovery process for oil-bearing subterranean formations penetrated by at least one production well and'by at least one injection well comprisinto the core followed by the 5 percent sodium chloride 5 g ag Oil p i g a ifpd due enltirely to a. injecting into said formation via an injection well t e a P oye an ca 6 tertiary i a slug of from 2 to 20 percent of the pore volume In Example 1, below, the additive was a slug of Sulfof the formation f a aqueous Solution of f nate A described above. The additive was followed by 0 to 10 percent by weight of a water soluble 5 percent sodium chloride b rme drive fluid. partially hydrolyzed polyacrylallnide polymer,

Example the afidmve a Polyacrylamlde b. injecting into said formation via an injection well thickened 5 percent sodium chloride brine followed by a slug 5 to 10 percent of the pore volume Sulfonate A wherein the sulfonate was not added as a of the formation of an aqueous solution of from 5 slug but rather was uniformly dispersed in the 5 percent to 50 percent by weight of a di n alkylbenzene sub Sodmm chlonde brme drive fonate having alkyl groups containing from ll to Examples 1 and 2 represent or] recovery techniques 15 carbon atoms ggt lg 2 33 4 5? "at th t h f th c. injecting into said formation via an injection well p e us 6 e cc mques o e an aqueous waterflood drive fluid, and stam Invention d. producing fluids from said formation via a produc- In Example 3 the additive was a mixture of polyacryltion we amide thickened 5 percent sodium chloride brine and 2 The recess of claim I wherein the S1 ofa ueous a concentrated slug of Sulfonate A in 5 percent sodium p q chloride brine followed by 5 percent sodium chloride solution of said polyacrylamide polymer is in ected into brine drive fluid the formation prior to the slug of aqueous solution of In Example 4 the additive was a slug of polyacryl- Sald Sulfonate amide thickened sodium chloride brine, followed by a T P F 1 f faqueus concentrated slug of Sulfonate A in 5 percent sodium solutlon ofsald polyzfcrylamjde Polymer f the Slug of chloride brine, followed by 5 percent sodium chloride 531d Sulfonate are mxed pnor to bemg m-lected brine drive fluid, 4. An oil recovery process following primaryproduc- It is readily apparent from these tests that the oil r tion for petroleum-bearing subterranean formations covery technique of this invention, as illustrated by Expenetrated by a plurality of wells comprising: amples 3 and 4, resulted in substantially more tertiary a. injecting into said formation via an injection well oil recovery than the prior art methods, as illustrated by a slug of a thickened aqueous solution,

Examples 1 and 2. b. injecting into said formation via said injection well TABLE I Cumulative pore volume tertiary oil recovered per cumulative pore volume of injected tertiary recovery additive (percent pore volume Example Tertiary recovery additive (percent pore volume) 0. 2 0. 4 0. 6 0. 8 1. 0 1. 2 1. 4 1. 0

2 Sulfonate A 0.0 0. 030 0.056 0. 064 0. 007 0. 067 0. 007 0. 067

8 polyacrylamide followed by 1.5 Sulfonate A dispersed in drive fluid 0.0 0.011 0.03 C. 044 0.052 0.060 0. 064 0. 005

8 polyaerylamide plus1.5 Sulfonate A, followed by drive fiuid 0. 006 0.085 0.10 0.112 0.114 0.114 0.115 0.115

8 polyacrylamide followed by 1.5 Sulfonate A and concentrated slug, 0.005 0.080 0.14 0.108 0.112 0.112 0.114 0. 114

followed by drive fluid.

1 Added as a solution of 500 parts per million 30 percent hydrolyzed polyaerylamide polymer in 5 percent sodium chloride brine.

a slug of a di-n-alkylbenzene sulfonate surfactant having alkyl groups containing from 11 to 15 carbon atoms,

c. injecting into said formation via an injection well a waterflood drive fluid, and

d. producing fluids from said formation via a production well. 

2. The process of claim 1 wherein the slug of aqueous solution of said polyacrylamide polymer is injected into the formation prior to the slug of aqueous solution of said sulfonate.
 3. The process of claim 1 wherein the slug of aqueous solution of said polyacrylamide polymer and the slug of said sulfonate are mixed prior to being injected.
 4. An oil recovery process following primary production for petroleum-bearing subterranean formations penetrated by a plurality of wells comprising: a. injecting into said formation via an injection well a slug of a thickened aqueous solution, b. injecting into said formation via said injection well a slug of a di-n-alkylbenzene sulfonate surfactant having alkyl groups containing from 11 to 15 carbon atoms, c. injecting into said formation via an injection well a waterflood drive fluid, and d. producing fluids from said formation via a production well. 